Null Checks and Optional Usage in Java

In real projects, missing null checks often lead to NullPointerException . This article first introduces basic null‑checking methods using java.util.Objects.nonNull(obj) , Hutool's ObjectUtil , or simple obj != null .

2. List null checks – Distinguish between a List being non‑null and its size being greater than zero. Common patterns include list != null && list.size() > 0 , list.isEmpty() , or using Hutool's CollUtil.isEmpty . The article shows the source of list.isEmpty() and warns that calling it on a null list still throws NullPointerException .

3. String null checks – When a String is null, calling equals(...) or length() throws NullPointerException . Several approaches are presented:

if(a == null || a.equals(""));

if(a == null || a.length() == 0);

if(a == null || a.isEmpty());

Additionally, Apache Commons StringUtils provides isNotBlank and isNotEmpty methods with example return values.

4. Optional – The Optional class is introduced to prevent NullPointerException . Creation methods ( .empty() , .of(T) , .ofNullable(T) ) and common operations ( isPresent() , ifPresent() , orElse() , orElseGet() , orElseThrow() , map() , flatMap() , get() ) are listed. Sample code shows the internal structure of Optional and typical usage in service layers, demonstrating how a single line with Optional can replace multiple null‑check statements.

5. Summary – Each null‑checking technique has its appropriate scenario; while chain‑style code with Optional can be elegant, it may reduce readability, so developers should choose based on project needs.